What is used to protect a direct sensing steam pressure gauge from damage from contact with steam?

Correct Answer: Option D — The installation of a siphon tube (pig-tail) oriented vertically in the entrance to the gauge.

A siphon tube (pig-tail) prevents live steam from entering the Bourdon tube, which would damage the internal mechanism. By condensing steam into water, the siphon creates a protective liquid seal. It must be oriented vertically to ensure the condensate remains trapped in the loop, effectively insulating the gauge.